Thermoplastic, conjugate fibers of PE/PP, PE/PET, PP/PET, and the like have been used for the surface layer in sanitary napkins and other such absorbent products, and in cleaning mops, the wiping components of wipers, and so forth. These thermoplastic, conjugate, continuous fibers are sometimes used in the form of a web obtained by spreading a continuous fiber bundle.
In a continuous fiber bundle, thermoplastic, conjugate, continuous fibers that have been crimped are bundled so as to stick together, and are in a state of high fiber density. When such a bundle is processed into the surface layer of sanitary napkins, the wiping components of wipers, and so forth, the manufacture of these products includes a step in which the thermoplastic, conjugate, continuous fibers that make up the fiber bundle are separated from one another in the width direction to increase the apparent width, which is known as an spreading step. The result of this spreading step is that the thermoplastic, conjugate, continuous fibers that were bundled together into a fiber bundle in a state of high fiber density are loosened from one another to obtain a web in a state of low fiber density. The surface layer of sanitary napkins, the wiping components of wipers, and so forth are manufactured from a web obtained in this way and having bulk and fiber density that are substantially uniform in the width direction.
Various methods have been employed to open a fiber bundle and obtain a uniform web. For example, Japanese Patent Application Publication (hereunder referred to as “JP KOKAI”) No. Hei 9-273037 discloses that a tow (fiber bundle) having an apparently existent crimp and/or latent crimp, a single filament size of 0.5 to 100 denier, a total denier of 10,000 to 300,000, and an apparently existent crimp of 10 to 50 crimps per 25 mm has a width that is within a favorable range during drawing and spreading, and can be spread uniformly at high speed. Nevertheless, there is a need for a fiber bundle that will yield a high-bulk web more efficiently, and for this high-bulk web.
JP KOKAI No. 2002-69781 discloses a method for spreading a tow (fiber bundle) by imparting tension to the tow between rolls with a speed differential, and then elastically contracting, and imparting elongation and contraction to the crimp, wherein a sliding plate is brought into contact with the tow between the rolls to shift the fibers in the feed direction and make them spread better. Nevertheless, this requires the installation of a sliding plate in the equipment, and bringing the tow and the sliding plate into contact complicates the work, and both of these lead to considerable increases in cost.
Thus, attempts at spreading a fiber bundle and obtaining a uniform web at high productivity have been made from the standpoints of both improving the fiber bundle (the material) and improving the spreading method. However, if we consider cost, ease of work, productivity, and the properties and performance of the resulting web and the finished products obtained from this web, a satisfactory method has yet to be found.